Internet Protocol (IP) telephone systems such as Skype have become commonplace in recent years. The IP telephone system can be used simply by installing an IP telephone application on a personal computer or other network terminal, where the IP telephone application is software developed by the IP telephone provider for originating and receiving calls and implementing voice communications. Skype, which offers a free IP telephone application and free calls, has particularly enjoyed much popularity. One factor enabling Skype to offer free calls may be its peer-to-peer communications, which eliminate the need for a server.
Japanese unexamined patent application publications Nos. 2005-192086 and 2005-080025 disclose related technologies for IP telephones.
However, IP telephone systems such as Skype cannot recognize data for another IP telephone terminal when communicating with the other terminal via an IP telephone call. Hence, even when the other caller is using an IP telephone terminal equipped with functions other than a telephone function, the user of the IP telephone terminal cannot take advantage of these functions. In other words, the resources of the IP telephone system are not effectively utilized and, therefore, are wasted.
The “Problems to Be Solved by the Invention” section of Japanese unexamined patent application publication No. 2005-192086 describes a convenient communication system in which a communication apparatus can execute a function not supported by the communication apparatus itself but possessed by another device. However, there is no description of a structure that can resolve the above problem, that is, how to recognize data for the other device and the functions possessed thereby.
Specifically, Japanese unexamined patent application publication No. 2005-192086 describes an IP telephone system having a server that registers information on network terminals. With this system, each transceiver terminal is provided with a function for referencing the information registered on the server. Therefore, the user can acquire information on other terminals and can transmit data that the other terminals can process.
This technology may be incorporated in an IP telephone system such as Skype by introducing a server into the system in order to register information on external terminals. The server could be referenced to acquire information on the external terminals. However, connecting to a server makes the system more complex and expensive, which would have a great impact on a system such as Skype that charges little or no usage fees.
The description in “0019” of Japanese unexamined patent application publication No. 2005-080025 asserts that a transmitting device transmitting images and a receiving device receiving the images can identify which communication method is supported by both parties using SDP media stream descriptions expanded by an SIP message, but this technology does not sufficiently resolve the problem described above.